The present invention relates to improvements in combustion by enhancing burning in two and four cycle internal combustion engines.
During combustion the air-fuel mixture is drawn into the engine through the intake port due to low pressure created by the descending piston. The controlled air-fuel mixture is compressed by the rising piston to a desirable cylinder pressure. The compressed gases are ignited through a spark plug located in the cylinder head before top dead center (TDC) resulting in a sharp increase in temperature and pressure inside the combustion chamber. The expanding gases push the piston down which turns the crank rolling and storing the energy in a flywheel to do useful work.
Flame velocity and degree of combustion have a direct bearing on power output, efficiency, fuel consumption, emissions, operating temperatures, sound and vibration levels, and reliability. The flame velocity and degree of combustion are related to the state of air-fuel mixture which is ignited by the spark plug.
Four stroke combustion chamber layouts include plain cylindrical form, bath tub type, wedged shape type, and hemispherical cross flow type.
The flat portion of the cylinder head close to the piston crown at top dead center (TDC) is known as the “squish area.” Generally, the trapped charge between the piston crown and the squish area nearing TDC is ejected towards the combustion chamber cavity causing turbulence prior to ignition. Higher compression ratios are possible with squish designs resulting in improved engine efficiencies. Turbulence in the charge can be also caused by inlet ports, their shapes, angles and surface finish which help to keep the air-fuel mixture in a homogeneous state at the point of entry only. Multipoint fuel injection basically atomizes fuel particles prior to entry on the intake stroke and achieves better combustion.
One purpose of squish design in internal combustion engines is to convert kinetic energy in the form of fluid flow into turbulent energy. As the piston reaches top dead center of the compression stroke, the air-fuel mixture located between the piston and the head is squished out and flows into the combustion chamber cavity. When the piston displaces the air-fuel mixture; it imparts kinetic energy into the mixture. As the squished air-fuel mixture flows into the combustion chamber cavity, the energy is converted to turbulence. The effect of the turbulence is to promote mixing of air and fuel into a more homogeneous mixture that burns more quickly and efficiently.
Two stroke engines have lesser volumetric efficiency due to obstructions in ports and short time/area available during intake and transfer phases. Due to the size, shape, and angles of the ports, the charge is in a higher state of turbulence when entering the two stroke cylinder than the four stroke cylinder. Four stroke engines require more ignition advance to operate efficiently due to the lower state of turbulence and a denser charge before combustion. The turbulence inside the cylinder and head mainly helps to maintain the air-fuel mixture in a gaseous state and prevent condensation of fuel droplets.
The squish area is normally placed in the outer circumference of the combustion chamber and are machined smooth. The squish area could be a flat or a tapered area or two separate squish areas on opposite sides. The squish areas are either flat or angled depending on the profile of the piston crown.
In principle, the piston on the upward stroke causes the compression to progressively increase. Nearing TDC, the gases around the squish area and the piston crown are pushed toward the combustion chamber cavity causing turbulence and improving flame propagation as ignition has occurred before TDC thereby greatly reducing pinging and detonation. Present day two stroke combustion chambers are hemispherical or “top hat” type with a circular or partial squish area. The spark plugs are located centrally or offset depending on the requirement.
Present day four stroke combustion chambers house the inlet and exhaust valves. Multiple valve layouts are standard in high performance designs. Partial or circular squish areas can be provided. The spark plug location depends on design and availability of space.
Cylinder heads are largely made of alloys of aluminum having steel inserts for valve seats. Basic designs typically are bath tub, wedged or double wedged with a flat roof or hemispherical cross flow type with inclined valve layouts.
Standard practice has been to have squish areas of 20% to 40% or more of the combustion chamber area which is either concentric or offset to the cylinder axis at close proximities to the piston crown, causing turbulence in two stroke engines. Depending on the number of valves and layouts, four stroke combustion chambers can be machined to provide the squish area resulting in a puff of mixture pushed towards the spark plug causing turbulence and resulting in better combustion.
Various methods for improving efficiencies of combustion in two and four stroke methods have been attempted. U.S. Pat. No. 5,065,715 which is incorporated herein by reference, discloses the use of a central bowl along with a plurality of discrete channels circumferentially spaced about the bowl where each of the channels opens into the bowl. One problem with this design is the extensive modifications to the piston. Additionally, it is believed that the bowl actually decreases efficiency.
The present invention does not contemplate heterogeneous charge compression ignition engine designs utilizing divided combustion chambers. The divided chamber engine (sometimes called a pre-combustion chamber or swirl chamber engine) has the compression volume divided in distinct chambers separated by a dividing passageway. The area between the piston and cylinder is called the main combustion chamber and the remainder of the combustion chamber area located in the cylinder head is called the antechamber, pre-chamber or swirl chamber. With this design, unlike a homogeneous charge engine, no fuel is pulled into the cylinder during the intake cycle, only air; fuel is directly injected into the antechamber late in the compression stroke. The function of the antechamber is to break up the liquid fuel mixing it with air from the cylinder late in the compression stroke.
There is a need for improving the efficiencies in two and four stroke homogeneous charge spark ignition internal combustion engines using modified pistons having at least one groove in the crowns.
While certain novel features of this invention shown and described below are pointed out in the annexed claims, the invention is not intended to be limited to the details specified, since a person of ordinary skill in the relevant art would understand that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation may be made without departing in anyway from the spirit of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.”